The invention is directed to ceramic pigments consisting essentially of a colorless matrix and color furnishing compounds which are bound in the matrix material as discrete particles or in the matrix lattice as color furnishing ions.
Ceramic pigments in which the color furnishing materials either are embedded as discrete particles in the matrix (occluded pigments) or are bound in the lattice of the matrix in ionic form (host lattice pigments) are known extensively. Normally, they are produced by heating the starting materials for the matrix and the color furnishing compounds in the presence of mineralizers. Generally, there are used fluorides, especially alkali fluorides, as mineralizers.
Thus, for example, according to Seabright U.S. Pat. No. 2,441,447, blue and green ceramic pigments are produced by heating zirconium oxide, silica, and vanadium pentoxide in the presence of a fluoride mineralizer at a temperature of 550.degree. to 1200.degree. C. The presence of a fluoride mineralizer indeed is not absolutely necessary, but then for production of the matrix, calcining must be carried out at substantially higher temperatures. However, working with fluoride mineralizers is undesired for environmental reasons.
Therefore, it was the problem of the present invention to find ceramic pigments consisting essentially of a colorless matrix and color furnishing compounds which are bound as discrete particles in the matrix material or as color furnishing ions in the matrix lattice, which correspond to the ceramic requirements such as glazing, light and temperature resistance and which do not require a fluoride mineralizer in their production.
The pigments can be prepared by calcining at an appropriate temperature, e.g., 550.degree.-1200.degree. C.